Subsonic small-caliber ammunition and bullet used in same

ABSTRACT

A bullet for use with a small caliber rifle comprises a jacket and a lead core provided within the jacket. The jacket is drawn from a copper alloy material. A bearing surface portion of the jacket has a nominal thickness less than about .010″ and the copper alloy material of at least the bearing surface portion of the jacket has a nominal hardness that is substantially greater than an as-drawn hardness of the copper alloy material of the bearing surface portion of the jacket.

FIELD OF THE DISCLOSURE

The disclosures made herein relate generally to ammunition for firearms and, more particularly, to subsonic ammunition for use with semi and fully automatic weapons.

BACKGROUND

The projectile (i.e., bullet) from a fired weapon, particularly a rifle, typically leaves the muzzle of the weapon at a speed that is greater than the speed of sound, i.e. a muzzle velocity of greater than approximately 1086 ft/sec. at sea level under standard conditions of temperature and pressure. Such a speed is referred to as being supersonic. Causing the bullet to achieve supersonic speed is advantageous because the faster a projectile travels, the flatter is its trajectory to its intended target. Also, faster speeds of projectiles tend to reduce the effects of lateral wind forces upon the path of the projectile to its intended target.

Due to supersonic speed of a projectile enhancing its accuracy of delivery to an intended target, it can be seen why it is desirable for projectiles to have a supersonic muzzle velocity. However, projectiles travelling at supersonic speeds generate an audible sound during their free flight, which can undesirably be used to locate the source of the weapon from which the projectile was fired. Under certain circumstances of military operations and/or police operations, it is desirable that the source of the weapon firing a projectile not be identifiable by the sound generated by the travelling projectile. Furthermore, for a projectile of a given shape and mass, it is sometimes desirable for muzzle velocity to be used in limiting the potential for the projectile to strike a down-range object in the case with the projectile misses or passes through its intended target.

In certain situations, one approach for mitigating adverse concerns relating to supersonic muzzle velocity is to restrict the speed of travel of the projectile to a subsonic speed (i.e., a muzzle velocity of less than approximately 1086 ft/sec. at sea level under standard conditions of temperature and pressure). In doing so, the projectile does not generate an audible sound during its free flight, thus limiting the potential for locating the source of the projectile. Additionally, subsonic flight reduces the distance that a projectile can travel, thereby limiting the potential for the projectile to strike down-range objects.

In semi-automatic and fully automatic weapons, pressure (i.e., energy) generated by firing of a round of ammunition serves to energize the weapon's bolt actuation mechanism. As such, implementing subsonic flight of a projectile in a manner that reduces pressure within a weapon's barrel bore can result in there being insufficient energy generated during combustion of the ammunition to cycle the bolt in a semi-automatic or fully-automatic weapon and/or to lock the bolt in its open position upon the firing of the last round in the weapons' magazine. In some cases, gas pressure provided at a gas port of a weapon can be increased to suitable energizes a bolt-actuation mechanism of the weapon through use of a sound suppressor to sufficient levels. However, removal of the sound suppressor renders such weapon inoperable in its semi-automatic and/or automatic modes of operation when such pressure-deficient rounds of ammunition are used.

Accordingly, subsonic ammunition that is capable of providing sufficient energy for cycling the bolt actuation mechanism of a semi-automatic or fully automatic weapon without the use of a sound suppressor is advantageous, desirable and useful.

SUMMARY OF THE DISCLOSURE

Embodiments of the present invention are directed to bullets and rounds of ammunition that are configured for use with small-caliber semi-automatic and automatic weapons. More specifically, small-caliber bullets and rounds of ammunition configured in accordance with embodiments of the present invention provide subsonic flight when discharged in a semi-automatic or fully-automatic weapon and provide sufficient barrel bore pressure characteristics for cycling a gas-energized bolt actuation mechanism of such semi-automatic or fully-automatic weapon without the use of a sound suppressor to augment gas pressure within the barrel bore of the weapon. Ammunition configured in accordance with the present invention is well suited for applications where firepower is more of a consideration than is stealth. Accordingly, embodiments of the present invention advantageously overcome one or more shortcomings associated with some conventional small-caliber subsonic rounds of ammunition.

In one embodiment of the present invention, a bullet for use with a small caliber rifle comprises a jacket and a lead core provided within the jacket. The jacket is drawn from a copper alloy material. A bearing surface portion of the jacket has a nominal thickness less than about 0.010″ and the copper alloy material of at least the bearing surface portion of the jacket has a nominal hardness that is substantially greater than an as-drawn hardness of the copper alloy material of the bearing surface portion of the jacket.

In another embodiment of the present invention, a round of ammunition configured for providing sufficient energy for cycling a bolt carrier in a rifle having a gas-energized bolt carrier actuation mechanism comprises a small-caliber cartridge casing, a bullet having a bearing surface portion thereof engaged within a bullet receiving opening of the small-caliber cartridge casing thereby forming a propellant-receiving cavity within the small-caliber cartridge casing, and a propellant within the propellant-receiving cavity of the small-caliber cartridge casing. The small-caliber cartridge casing is configured in accordance with an original equipment manufacturer (OEM) specification for the rifle. The bullet has a core made of a metal having lead as its major constituent component and a jacket drawn from metal having copper as its major constituent component. A nominal thickness of the jacket is less than about 0.010″. At least the bearing surface portion of the jacket has a nominal hardness that is substantially greater than an as-drawn hardness of the jacket. The propellant is configured by a manufacturer thereof for being used in medium caliber ammunition.

In another embodiment of the present invention, a method for making a bullet for use with a small caliber rifle comprises providing a jacket having a thickness less than about 0.010″, forming a lead core within a core-receiving cavity of the jacket, and hardening at least a bearing surface portion of the jacket to have a nominal hardness that is substantially greater than an as-drawn hardness of the jacket after forming the lead core within the core-receiving cavity of the jacket. The jacket is drawn from a copper alloy material.

These and other objects, embodiments, advantages and/or distinctions of the present invention will become readily apparent upon further review of the following specification, associated drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a round of ammunition configured in accordance with an embodiment of the present invention.

FIG. 2 is a fragmentary cross-sectional view of the round of ammunition of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWING FIGURES

Referring now to FIGS. 1 and 2, a round of ammunition 100 configured in accordance with the present invention is shown. The round of ammunition 100 is configured for use with small-caliber semi-automatic and automatic weapons (e.g., a rifle). Advantageously, the round of ammunition 100 is configured to provide subsonic flight when discharged in a semi-automatic or fully-automatic weapon and to provide sufficient gas pressure characteristics for cycling a gas-energized bolt actuation mechanism of such semi-automatic or fully-automatic weapon without the use of a sound suppressor to augment gas pressure. In doing so, the round of ammunition 100 advantageously overcomes a key shortcoming associated with some conventional small-caliber subsonic rounds of ammunition.

The round of ammunition 100 includes a small-caliber cartridge casing 102 configured in accordance with an original equipment manufacturer (OEM) specification for a weapon. The small-caliber cartridge casing 102 includes a first end portion 104 and a second end portion 106. Typically, a primer is mounted within the second end portion 106 thereby making the second end portion substantially closed. Preferably, but not necessarily, the small-caliber cartridge casing 102 can be made a metal material (e.g., brass) or from a polymeric material (e.g., nylon).

Standards for the shape and size of a cartridge for a certain weapons of a given caliber have been established and published by Sporting Arms and Ammunition Manufacturers Institute (SAAMI). A rifle of the M4/M16/AR15 family of carbine rifles is a weapon that is capable of being operated in a semi-automatic mode and/or fully-automatic mode and that utilizes barrel bore pressure resulting from discharge of a round of ammunition to energize a bolt actuation mechanism of the weapon. Thus, in one embodiment, the round of ammunition 100 can be configured for use with a rifle of the M4/M16/AR15 family of carbine rifles. However, in view of the disclosures made herein, it is disclosed that a skilled person will appreciate other weapons for which a round of ammunition configured in accordance with the present invention will be useful and that embodiments of the present invention are not unnecessarily limited to use with any particular weapon (i.e., any particular rifle, piston, or other type of small-caliber firearm).

The round of ammunition 100 has a bullet 108 (i.e., a projectile) with a bearing surface portion 110 engaged within a bullet receiving opening 112 of the small-caliber cartridge casing 102. The bullet receiving opening 112 is located at the first end portion 104 of the small-caliber cartridge casing 102. In this manner, a propellant-receiving cavity 114 is formed within the small-caliber cartridge casing 102 between its first and second end portions 104, 106. An ogive portion 116 (i.e., contoured tip portion) of the bullet 108 extends beyond the bullet receiving opening 112 and, optionally, some of the bearing surface portion can also extend beyond the bullet receiving opening 112.

As shown in FIG. 2, the bullet 108 has a core 118 made of a first type of metal disposed within a core-receiving cavity 119 of a jacket 120 made of a second type of metal. A jacket configured in accordance with the present invention can be made by the process of drawing metal (e.g., a sheet of metal) into a given shape and the bearing surface portion 110 can have a thickness of less than about 0.010″. In a preferred embodiment, the bearing surface portion 110 has a nominal thickness between about 0.004″ and about 0.008″. Preferably, but not necessarily, the jacket 120 is made from a copper alloy including about 90% copper (Cu) and up to about 10% zinc (Zn) and the core 118 is made from a metal having lead as its major constituent component. In a preferred embodiment, the jacket 120 is made from a copper alloy having a minimum of about 2% zinc.

The bearing surface portion 110 and, optionally, the ogive portion 116 have a nominal hardness that is substantially greater than an as-drawn hardness of the jacket 120. In a preferred embodiment, the jacket 120 is drawn from a copper alloy material having a tensile strength substantially below about 32 ksi. Subsequent to the jacket 120 being drawn and the core 118 being formed within the core-receiving cavity 119 of the jacket 120, the bearing surface portion 110 and optionally the ogive portion 116 are hardened to have a tensile strength greater than about 32 ksi. In a preferred embodiment, the bearing surface portion 110 and optionally the ogive portion 116 are hardened to have a tensile strength between about 32 ksi and about 44 ksi. Optionally, the finished hardness specification for the copper alloy material can be specified as between about one-eighth hard and about one-half hard with respect to the copper alloy material being “dead soft”. As such, it is disclosed herein that, after forming the core 118 within the core-receiving cavity 119 of the jacket 120, the bearing surface portion 110 of the jacket 120 and optionally the ogive portion 116 preferably have a nominal hardness that is substantially greater than an as-drawn hardness of the jacket 120.

Examples of means for hardening the jacket 120 include, but are not limited to, shot peening, ultrasonic hardening, and the like. In the case where the jacket is shot peened, the jacket 120 and the shot (e.g., steel shot) can optionally be exposed to a friction-reducing material composition during such shot peening so that the shot peening causes at least a portion of an exterior surface 122 of the jacket 120 to become coated with a layer of friction-reducing material composition. Molybdenum disulfide is one example of a friction-reducing material composition (i.e., a lubricant) to which the jacket 120 and the shot (e.g., steel shot) can be exposed during such shot peening for causing the exterior surface of the jacket 120 to become coated with a layer of friction-reducing material composition (i.e., a layer of molybdenum disulfide).

As shown in FIG. 2, the round of ammunition 100 has a propellant 124 (e.g., powder) within the propellant-receiving cavity 114. The propellant 124 can be a relatively slow burning type propellant that provides a rapid peak in pressure build up within the propellant-receiving cavity 114 and that maintains a broader burn duration than relatively fast burning type propellants. In one embodiment, the propellant 124 is configured by a manufacturer thereof for being used as a medium caliber ammunition propellant. One example of such a medium caliber propellant suitable for use with rounds of ammunition configured in accordance with the present invention has been offered from General Dynamics Corporation under propellant no. XPR 47C1. In view of the disclosures made herein, a skilled person will appreciate that other propellants of suitable specification can be used in rounds of ammunition configured in accordance with the present invention.

During firing of the round of ammunition 100 within a weapon, the propellant 124 in combination with the bullet 108 result in gas pressure characteristics and bullet-bore frictional characteristics that provide for subsonic flight of the bullet 108 and for sufficient gas pressure within a barrel bore of the weapon to cycling a gas-energized bolt actuation mechanism of the weapon. For a given configuration of ammunition (e.g., 5.56 mm NATO ammunition), the bullet 108 will be heavier (e.g., by as much as 12 grains) than a bullet with a standard thickness drawn-metal jacket in view of the relatively thin jacket 120 and greater volume of the core 118. When this relatively heavy, thin-jacket bullet 108 is subjected to the heat and pressure of discharge of the propellant 108, the relatively thin jacket 120 and the relatively large core 118 will result in enhanced obturation of the bearing surface portion 110 of the bullet 108 within the barrel bore of the weapon such that sliding friction between the bearing surface portion 110 and barrel bore will be enhanced relative to a comparable bullet of conventional (i.e., prior art) construction.

Sliding friction between the bore and the bullet 108 creates heat in the jacket 120. The lead of the core 118 has relatively low heat conductivity and the copper alloy of the jacket 120 has relatively high heat conductivity. Heat produced within the jacket 120 will penetrate the full thickness of the jacket 120 within the time it takes for the bullet 108 to pass down a length of the barrel bore of the weapon. When this heat reaches the core 118, the core 118 serves as an effective insulator thereby causing more heat to building the jacket 120 and, thus, soften the jacket 120 further to provide for more sliding friction. Roughly speaking, given identical frictional heating, a jacket that is three times as thick as a thinner jacket will heat up about one-third of the amount that the thinner jacket will heat up. The friction coefficient of copper is a strong function of the surface hardness and hardness is a strong function of temperature. In this manner, the jacket 120 being relatively thin further enhances sliding friction between the bearing surface portion 110 and the barrel bore. In combination with these frictional and obturation considerations of the bullet 108, the propellant 124 provides gas pressure characteristics (e.g., peak gas pressure, percent dwell around peak gas pressure, and average gas pressures) within the barrel bore of the weapon to generate sufficient gas-pressure derived energy at a gas port of the weapon for cycling its bolt carrier when the round of ammunition 100 is discharged. These gas pressure characteristics in combination with weight of the bullet 108 and frictional forces exerted on the bullet 108 causes the bullet 108 to decelerate from a supersonic speed (e.g., at a barrel position where the gas port is located) to a subsonic speed prior to exiting the barrel bore.

It is disclosed herein that the use of a layer of friction reducing material on the bearing surface portion 110 of the bullet 108 can be used to influence gas pressure characteristics and/or resulting velocity profile of the bullet 108. For example, as disclosed above, molybdenum disulfide is one example of a friction-reducing material composition to which the jacket 120 and the shot (e.g., steel shot) can be exposed during such shot peening for causing the exterior surface of the jacket 120 to become coated with a layer of molybdenum disulfide. Coating the bearing surface portion 110 with a layer of molybdenum disulfide or other suitable friction reducing material composition can result in the bullet exhibiting reduced initial friction in the barrel bore, with diminishing effect as velocity of the bullet 108 increases (e.g., provides negligible effect with suitable velocity). Thus, its application to the bearing surface portion 110 of the bullet 108 can result in lower initial gas pressure, which moderates and broadens the initial gas pressure spike produced by combustion of the propellant 120. In effect, such a layer of friction reducing material can delay onset of heating of the jacket and thus influence sliding friction as a function of time.

It is disclosed herein that configuring a round of ammunition in accordance with the present invention can include manipulating ammunition-specific parameters including, but not limited to, jacket thickness, jacket material composition, jacket hardness, bearing surface length, core material composition, propellant type, propellant quantity, and jacket surface coating presence/type. All or a portion of these ammunition-specific parameters can be manipulated in view of weapon-specific parameters including, but not limited to, barrel bore diameter, barrel bore length, gas port position/size, required bolt actuation mechanism energy, barrel bore material, etc. In view of the disclosures made herein, a skilled person will be able to specify ammunition-specific parameters for ammunition configured in accordance with the present invention for a particular configuration of weapon (e.g., a rifle) by experience and/or with minimal experimentation.

In the preceding detailed description, reference has been made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the present invention may be practiced. These embodiments, and certain variants thereof, have been described in sufficient detail to enable those skilled in the art to practice embodiments of the present invention. It is to be understood that other suitable embodiments may be utilized and that logical, mechanical, chemical and electrical changes may be made without departing from the spirit or scope of such inventive disclosures. To avoid unnecessary detail, the description omits certain information known to those skilled in the art. The preceding detailed description is, therefore, not intended to be limited to the specific forms set forth herein, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents, as can be reasonably included within the spirit and scope of the appended claims. 

1. A bullet for use with a small caliber rifle, comprising: a jacket drawn from a copper alloy material, wherein a bearing surface portion of the jacket has a nominal thickness less than about 0.010″ and wherein the copper alloy material of at least the bearing surface portion of the jacket has a nominal hardness that is substantially greater than an as-drawn hardness of the copper alloy material of the bearing surface portion of the jacket; and a lead core provided within the jacket.
 2. The bullet of claim 1 wherein the bearing surface portion of the jacket is at least partially coated with a friction-reducing material composition.
 3. The bullet of claim 2 wherein the friction-reducing material composition is molybdenum disulfide.
 4. The bullet of claim 3 wherein the bearing surface portion is coated in its entirety with the friction-reducing material composition.
 5. The bullet of claim 1 wherein the nominal hardness of the copper alloy material of at least bearing surface portion corresponds to a tensile strength of between about 32 ksi and about 44 ksi.
 6. The bullet of claim 5 wherein the bearing surface portion of the jacket is at least partially coated with a friction-reducing material composition.
 7. The bullet of claim 6 wherein the friction-reducing material composition is molybdenum disulfide.
 8. The bullet of claim 7 wherein the bearing surface portion is coated in its entirety with the friction-reducing material composition.
 9. The bullet of claim 5 wherein the bearing surface portion of the jacket has a thickness between about 0.004″ and about 0.008″.
 10. The bullet of claim 1 wherein the bearing surface portion of the jacket has a thickness between about 0.004″ and about 0.008″.
 11. A round of ammunition configured for providing sufficient energy for cycling a bolt carrier in a rifle having a gas-energized bolt carrier actuation mechanism, comprising: a small-caliber cartridge casing configured in accordance with an original equipment manufacturer (OEM) specification for the rifle; a bullet having a bearing surface portion thereof engaged within a bullet receiving opening of the small-caliber cartridge casing thereby forming a propellant-receiving cavity within the small-caliber cartridge casing, wherein the bullet has a core made of a metal having lead as its major constituent component and a jacket drawn from metal having copper as its major constituent component, wherein a nominal thickness of the jacket is less than about 0.010″, and wherein at least the bearing surface portion of the jacket has a nominal hardness that is substantially greater than an as-drawn hardness of the jacket; and a propellant within the propellant-receiving cavity of the small-caliber cartridge casing, wherein the propellant is configured by a manufacturer thereof for being used in medium caliber ammunition.
 12. The round of ammunition of claim 11 wherein the bearing surface portion of the jacket is at least partially coated with a friction-reducing material composition
 13. The round of ammunition of claim 12 wherein the friction-reducing material composition is molybdenum disulfide.
 14. The round of ammunition of claim 13 wherein the bearing surface portion is coated in its entirety with the friction-reducing material composition.
 15. The round of ammunition of claim 11 wherein the nominal hardness of said jacket metal of at least the bearing surface portion corresponds to a tensile strength of between about 32 ksi and about 44 ksi.
 16. The round of ammunition of claim 15 wherein the bearing surface portion of the jacket is at least partially coated with a friction-reducing material composition.
 17. The round of ammunition of claim 16 wherein the friction-reducing material composition is molybdenum disulfide.
 18. The round of ammunition of claim 17 wherein the bearing surface portion is coated in its entirety with the friction-reducing material composition.
 19. The round of ammunition of claim 15 wherein the bearing surface portion of the jacket has a thickness between about 0.004″ and about 0.008″.
 20. The round of ammunition of claim 11 wherein the bearing surface portion of the jacket has a thickness between about 0.004″ and about 0.008″.
 21. A method for making a bullet for use with a small caliber rifle, comprising: providing a jacket having a thickness less than about 0.010″, wherein the jacket is drawn from a copper alloy material; forming a lead core within a core-receiving cavity of the jacket; and hardening at least a bearing surface portion of the jacket to have a nominal hardness that is substantially greater than an as-drawn hardness of the jacket after forming the lead core within the core-receiving cavity of the jacket.
 22. The method of claim 21 wherein said hardening includes shot peening the jacket with steel shot.
 23. The method of claim 22, further comprising: exposing the jacket and the steel shot to a friction-reducing material composition during said shot peening such that said shot peening causes at least a portion of an exterior surface of the jacket to become coated with a layer of the friction-reducing material composition.
 24. The method of claim 23 wherein the friction-reducing material composition is molybdenum disulfide.
 25. The method of claim 21 wherein the nominal hardness of the copper alloy material of at least the bearing surface portion corresponds to a tensile strength of between about 32 ksi and about 44 ksi after performing said hardening.
 26. The method of claim 25 wherein said hardening includes shot peening the jacket with steel shot.
 27. The method of claim 26, further comprising: exposing the jacket and the steel shot to a friction-reducing material composition during said shot peening such that said shot peening causes at least a portion of an exterior surface of the jacket to become coated with a layer of the friction-reducing material composition. 